Electrodeposition of chromium



Patented June 30, 1925.

UNITED STATES ,544,451 ATENT CARL HAMBUECHEN, OF MOUNT VERNON, NEW YORK,ASSIGNO'R TO IEJLE(HERO METALLURGICAL COMPANY, A CORPORATION OF WESTVIRGINIA.

ELECTRODEPOSITION OF CHROMIUM,

N Drawing.

To allwlaom it may concern: Be it known that I, CARL HAMBUEQHEN, acitizen of the United States, residing at .Mount Vernon, in the countyof Westchester 5 and State of New York, have invented certain new anduseful Improvements in Electrodepo si tion of Chromium, of which the 1following is a specification.

I The invention is a process for electrodein positing chromium. Theobject is to provide an improved process easier of execution and capableof giving deposits of better quality. This object is attained by the useof an electrolyte of novel composition. A is novel arrangement of anodesis also included in the invention. v

As electrolyte I employ an aqueous solution of chromic acid to which hasbeen added asmall quantity of a fiuorid, such as chromium, iron,ammonium or sodium fluorid. The electrolyte is preferably free fromstrong. mineral acids such as sulphuric and hydrochloric.

To prepare the electrolyte I merely dissolve pure chromic acid in waterin the proportion of about 200 to 600 grams per liter 'of s'olution, andadd about 10 to 50 grams of sodium .fluorid or an amount of anothermetal fluorid containing an equal quantity of fluorin to each liter ofthe solution. Very good results have been obtained .with an electrolytecontaining 300 grams of CrO per literl The deposition may be carried outat room temperature or above. Temperatures below C.

.peres per square foot have given good '-results "If a small amount ofsulphuric acid is added; to electrolyte prepared as described above,-the electrolyte does not become totally inoperative, but the currentefiicienc'y is" fiuorin had been, added, in one 1 case; as

. sodium fluorid and in the other case as hydrofluoric acid werecompared, "The-cursrent efficiency ofthe. sodium" -fluo'rid bath: 4 {wasalmost double-that o he t r h tawh'ile'the voltage required was muchless Application filed. July 5, 1924. Serial No. 724,515.-

than half.

are preferred. Cathode current densities of 50 to 300 'am-.,

[cathode-surface.

claim! 1. Abath forelectrodepositing'chromium,

The bath containing hydro fiuoric acid accordingly consumed more thanfour times as much power per gram of chromium deposited. I

The electrolyte of my invention can be assure used in-conjunction withinsoluble anodes of materials such 'as lead and lead peroxid.

It is of course necessary to replenish the bath from time to time withadditions of chromic acid. In attempting to operate with chromiumanodes, I have found that the current efliciency at the anode greatlyexceeds that at the cathode, causing the chromium content of the bath toincrease continuously, raising the voltage, and diminishing the currentefficiency. The same effect has been observed with other electro-. lytesproposed for the deposition of chromium. I avoid this difficulty by theuse of both insoluble anodes and soluble chromium anodes.

them in the bath simultaneously. It is impossible to state what ratio ofinsoluble anode surface to soluble anode surface will maintain the bathin constant conditionunder all circumstances, since this ratio may varywith the desired chromium concentrationin the bath, with the anodecurrent density and its relation to the cathode current density, withthe temperature of the bath, etc. The proper ratio for a particulararrangement is readily found by trial. With a chromium anode having asurfacev equal to the cathode surface, anode current eflicien ciesabout. six times' asgreat'as the cathode: current efliciency have oftenbeen observed.'

as lead, is therefore indicated, and has been approximately equal to theHaving. now. described my invention, jI

containing I c'hromie aciv in ,e rcess anda soluble metal fluor1d, andbe ng substans The replacement of about five-sixths of the anode surfacewith insoluble material, such tially free from acids other than chromic.2. A bath for electrodepositing chromium containingper liter 200 to 600grams. of

chromic acid and 10 to 50 grams of an alkali metal fluorid, andbeingsubstantially free from acids other than chromic.

3. A bath for electrodepositing chromium containing chromic acid and 10to 50' grams of sodium fiuorid per liter, and being subs stanti-allyfree from acids other than chromic, and from sulphates.

4. Process of electrode ositing chromium from a bath containing 0 romicacid which comprises passing the depositing current into the baththrough a soluble anode containing chromium, and an insoluble anode,

and adjusting the surfaces of the two anodes and the times of theirimmersion to main tain an efiicient concentration of chromium in thebath. 5. Process of electrodepositing chromium from a bath containingchromic acid which comprises passing the depositing current into thebath simultaneously-through a solubl e anode containing chromium, and aninsoluble anode, and adjusting the surfaces of 7.. Process ofelectrodepositing chromium from a bath containing chromic acid and analkali metal .fluorid, which comprises assing the depositing currentinto the ath through a soluble anode containing chromium, and aninsoluhle anode, and adjust-- ing the surfaces of the'twoj anodes andthe times of their-immersion to maintain an gflicientconcentration ofchromium in the ath.

8; Process of electrode ositing chromium from a bath containing 0 romicacid and a metal fluorid, which comprises passing the de ositing currentinto the bath through a so uble anode containing chromium, and aninsoluble anode, and adjustingvthe surfaces of the two anodes and thetimes. of their immersion to maintain an efiicient concen-v tration ofchromium in the bath. H In testimony whereof I 'afiizrmy signature. I

CARL HAMBIIZJEOHEN.

